186 PRACTICAL ORGANIC CHEMISTRY
3. Dissolve naphthalene in a little spirit, and add an
equal quantity of a solution of picric acid in spirit. Or*
cooling, yellow needles of naphthalene picrate separate,
C10Hg.CcH2OH(NO2)3. Benzene forms colourless crystals,
anthracene, scarlet needles, having a similar composition. See
Appendix, p. 295.
Baeyer, Ber., 1876, 9, 1230, and Annalen, 1880, 202, 68,
10 grms. phthalic anhydride.
20 „ phenol.
8 „ cone, sulphuric acid.
The phthalic anhydride, phenol, and concentrated sulphuric
acid are heated together to 115—120° in the oil-bath 8—9 hours.
The mass becomes semi-fluid and of a dark red colour. It is
poured, whilst hot, into a basin of water (500 c.c.) and boiled.
until the smell of phenol has disappeared, the water being"
renewed as it evaporates. The undissolved yellow granular
precipitate, on cooling, is separated from the liquid by filtration,
and washed with water. It is then dissolved in dilute caustic
soda solution, filtered from the undissolved residue, and tlie
filtrate acidified with acetic acid and a few drops of hydro-
chloric acid. The phthalein separates out, after standing for
some hours, as a light yellow, sandy powder, which is filtered
and dried. It is purified by dissolving in absolute alcohol witli
the addition of animal charcoal (i part phenolphthalein, 6 parts
alcohol, and \ part charcoal) and boiling the solution on ttoe
water-bath for an hour. The mass is filtered hot, washed witli
2 parts boiling alcohol, and the filtrate evaporated down to
two-thirds its bulk on the water-bath. On adding 8 times trie
quantity of cold water to the cooled solution, the latter becomes
turbid. The liquid is well stirred, and, after standing a few
seconds, filtered through cloth from the resinous oil whicli
separates. On heating the filtrate on the water-bath to expel